1. Field of the Invention
The present invention relates to airflow measurements and instruments for measuring airflow.
2. Background of the Related Art
An airflow bench is a testing system used to flow air through a unit to be tested (i.e. a “unit under test”) to determine the aerodynamic properties of the unit under test. Airflow through a unit, such as computer chassis, is important since the airflow may be responsible for cooling heat-generating devices within the unit. An airflow bench typically includes an air moving device to drive airflow through the unit under test and an airflow measuring device to measure the airflow rate through the unit under test. The measured airflow rate can then be used to evaluate the aerodynamic properties and or thermal properties of the unit. For example, the airflow impedance of the unit under test may be determined based on the measured airflow rate.
Conventionally, the airflow rate is determined according to a pressure difference measured across a nozzle or orifice plate between the two air collection boxes. The first (inlet) collection box is used to collect air output from the unit under test and direct the collected air to the nozzle or orifice plate. The air from the first collection box flows through the nozzle or orifice plate and exits into the second (outlet) collection box. The second collection box guides the air into the air moving device to exhaust the air from the airflow bench. In such an arrangement, the air expands and contracts repeatedly. Specifically, the air expands through the first collection box, contracts through the nozzle or orifice plate, re-expands in the second collection box, and then contracts again into a blower assembly before being exhausted from the airflow bench.